The present invention relates to remote-control systems. The invention is particularly useful in control of electrical devices in a building and in control of appliances.
Conventional switches used in building electrical power systems are connected in the power supply wiring of the building between the power source and the loads controlled by the switches. Accordingly, the power wiring of the building must extend to each switch and from each switch to the load. An ordinary wall switch controlling a ceiling light fed by an electric power wire in the ceiling thus requires a branch extending down from the ceiling through the wall to the switch and back up through the wall to the light fixture. Such branch wiring requires expensive materials, such as high voltage cable, junction boxes and the like, to handle the electrical power. Moreover, expensive, skilled labor is required to install such branches during construction of the building. Even more labor is required to install such a switching branch in a completed building, where the branch wiring must be worked through existing walls.
All of these problems are even more severe where a load must be controlled from more than one switch. The conventional "three way" switch arrangement utilized to control a ceiling light from either end of a stairway requires a switching branch extending from the power supply wiring to one switch, from that switch to the other switch and from the other switch to the light. Where a single load is to be controlled by more than two switches, the required interconnections become even more complex and costly.
Low voltage remote control systems bring only low voltages to the switches and use the switched low voltage to control relays or other high voltage switching devices in the building wiring system. These systems eliminate the need for high voltage components in the switching branches, but do not eliminate the need for a wired connection between the switch and the controlled device. Therefore, substantially the same labor costs are involved in installation of these systems. Moreover, the relays required at the controlled devices add significant costs.
Another remote control system which has been utilized to some extent in building wiring is the "carrier current" system. In the carrier current system, the control switch actuates a small radio frequency transmitter which is connected to the building wiring so that the radio signal propagates through the wiring to a receiver mounted on the controlled device. The receiver actuates a relay or electronic switch controlling the power flow to the device. Each transmitter must be directly connected to the wiring, thus restricting the versatility of the system and adding to its cost. Moreover, carrier current systems typically convey information only at relatively low rates and typically can control only a few devices in a given system. There is a considerable possibility of interference between multiple carrier current systems as, for example, where carrier current systems are used in multiple homes served by a common supply transformer. Conversely, carrier current systems cannot pass information between locations served by different supply transformers, and hence are unsuitable for use in large buildings with multiple supply transformers. Also, carrier current systems typically encounter difficulties with spurious signals caused by random electrical noise on the power line. These and other difficulties have limited application of carrier current systems.
Attempts have been made heretofore to eliminate the difficulties associated with wired and carrier current systems by using free space communication for control purposes, i.e., by directing the control signal from a transmitter through free space within the building to a receiver at the fixture. With free space propagation, the transmitter location is unrestricted and the costs of switch wiring are eliminated. Control signals can in theory be propagated through free space as acoustic signals such as ultrasonic waves or as optical signals, i.e., light beams. These techniques are used in limited applications such as television remote controls and the like where there is only a short gap between the transmitter and receiver and where there is direct line of sight communication between the two. As these favorable conditions are not always present in a building wiring control system, these acoustic and optical systems typically are unsuitable for controlling electrical power within a building.
Attempts have been made to utilize radio control systems for certain limited aspects of building power and/or appliance control as, for example, garage door openers, individual power outlet controls and the like. These systems, however, have been unreliable inasmuch as they are subject to unintended actuation by interfering radio transmitters and, conversely, sometimes fail to actuate the controlled device. To avoid interference with other radio equipment, the transmitters used in these radio control systems are required to be low power devices, thus limiting the range of the system. Additionally, the transmitters and receivers used in these radio control devices have not been suited for mounting within the junction boxes normally used in electrical wiring systems. These junction boxes often are metal enclosures which tend to attenuate radio signals. To receive the weak signals provided by the low powered transmitters, the receiver must either be mounted outside of the junction box or provided with an antenna structure extending out from the box, rendering the entire device cumbersome and unsightly. Moreover, most radio control systems available heretofore have required expensive components. For all of these reasons, radio control systems have not been widely adopted in building wiring systems.
Thus, although there has been an acute need for an inexpensive, reliable and versatile wireless or free space power control system suitable for use in a building power system, no such control system has been available heretofore. The same need for a reliable remote control system exists in the case of thermostats, doorbells and other devices which must actuate another unit at a remote location. There is a similar unmet need with respect to wireless control systems for appliances. Although appliances have been provided heretofore with the short range, line of sight optical and acoustic remote control systems mentioned above, and with rudimentary, unreliable radio control units, there has been no truly satisfactory system for wireless remote control of electrical appliances. The need with respect to remote control of appliances has become more acute with the advent of home automation systems. Modern data processing technology can provide a central automation system capable of controlling and coordinating many appliances within the home, and also coordinating building fixtures such as lights, heaters and alarms. Heretofore, the difficulty and expense of communication between the central system and the various appliances has hindered adoption of such systems.